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How to tell what a function is returning
Posted: Sun Feb 07, 2021 4:32 pm
by bogs
In a recent topic I posted about the 'selectedLine', I found out that the information returned is in the form of a string (for which I thank the contributors very much!!).
What I would like to know is, how do you tell if what is being returned is a string, vs. not a string heh.
*Edit - I couldn't see any way to differentiate for instance stepping through a handler and looking at the return in the variables.
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 4:52 pm
by FourthWorld
Most values in LC are strings. The only exception i can think of offhand is an array, which can be tested with "...is an array".
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 4:52 pm
by richmond62
Code: Select all
on mouseUp
put cheese (123) into ABC
if ABC is not an integer then
put "string"
else
put "numeric"
end if
end mouseUp
function cheese XYZ
return "He's a sausage"
end cheese
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 5:09 pm
by bogs
Hmm. I'll live with being a cheesey sausage, but for instance, if I set the loc of something to the mouseLoc, it will go to that location without needing something like 'the value of ' or like that.
I guess what I'm trying to understand is, how come certain functions can be treated like that, where others can not be?
To compare apples to apples in this context, the selectedChunk can be used directly, the selectedLine can not. How do you tell the difference in your script between the two?
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 6:08 pm
by richmond62
the selectedChunk can be used directly, the selectedLine can not
Well . . . as both a
selectedChunk and a
selectedLine can contain text then playing around with
integer is not going to help much.
So, surely, the way to tell them apart is to see whether they can be used directly (but, I do not understand what you mean by "used directly").
-
This silly little stack contains a text field above a scrolling list field. The text field has this in its script:
Code: Select all
on mouseUp
put the selectedChunk into fld "fOUTPUT"
end mouseUp
and NOTHING ends up in fld "fOUTPUT"
The scrolling list field has this in its script:
Code: Select all
on mouseUp
put the selectedLIne into fld "fOUTPUT"
end mouseUp
and, as you can see from the screenshot, something does end up in the fld "fOUTPUT".
That might be sufficient to differentiate selectedChunk from selectedLine: although, as those are dependent on the type of field
that the user mucks around in I cannot see why that is necessary.
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 6:25 pm
by richmond62
Of course you could use my earlier 'integer' bit of rocket science to work out if a selectedLine contains "Yakketty-Yak" or "987654321".
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 7:25 pm
by bogs
richmond62 wrote: ↑Sun Feb 07, 2021 6:08 pm
Well . . . as both a selectedChunk and a selectedLine can contain text then playing around with integer is not going to help much.
I must not be very clear in what I am asking, and for that I apologize.
The selectedLine returns a format : line x[lineNumber] of field y[fieldNumber].
The selctedChunk returns a format : startCharacter, endCharacter, or, alternately, it reports the insertion point location. As an example, the selectedChunk in the following:
Code: Select all
put the functionNames into field 2 |
would be
When I say you can use that directly, I mean that it can be referenced as is, where as if you wrote:
Code: Select all
put the last word of the selectedLine
you would see the field number as the last word, instead of the last word of the line the selectedLine is referencing. Does that make it any clearer?
Some selected functions seem to work one way, others completely differently, and since Richard says the vast majority of them return strings, I am trying to understand how to tell which of the two returns your getting without trying to memorize every function in Lc.
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 8:24 pm
by bogs
Mark W. actually put one part of it better than I did in a
bug report -
Mark Wieder 2008-04-21 12:09:37 EDT wrote:
Some object selectors need the qualifier "of something" while others don't. The
selectors that don't need the qualifier just ignore it if it's supplied. This
creates confusion not just among new rev developers, but also among seasoned
developers who have to remember which commands work which way. It would be useful
if all the selectors accepted an object qualifier; or secondly if the compiler
would at least give a compile-time error if the qualifier is supplied but would be ignored.
Commands that require an object qualifier:
the selectedText of...
the hilitedLine of...
Commands that ignore the object qualifier:
the selectedLine
the clickLine
the foundLine
the mouseLine
the selectedChunk
the selectedField
Just like the qualifier telling you
where to look (of field, of text), some of these need a pre-qualifier (like the text of, or the value of), while others don't and I am finding that hard to figure out.
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 10:25 pm
by dunbarx
Bogs.
Earlier, you either forgot, or did not know that if you had a field 1 with a selection, and you asked for:
you got the last word of the string that comprised the result of that function, an integer. But I think you wanted:
Code: Select all
the last word of line (word 2 of the selectedLIne) of fld 1
the last word of the line selected in the field.
So is the issue understanding the rather important difference between those two statements? If you read what the selectedLine actually returns, you can see that it gets its result from examining the field, but does not get anything "out" of the text of that field. For that you need to deconstruct what the selectedLine really gives you, and wrap other stuff around it and use that data to access certain contents of the field itself.
I hope I did not make this worse.
Craig
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 10:44 pm
by bogs
I did remember Craig, I think I must just be phrasing my question really poorly heh.
If I pull the information of a function, I (generally) expect to be able to use that information directly. For instance, if I pull the mouseLoc, and I want to set the loc of something to it, I would type:
Code: Select all
set the loc of [myObject] to the mouseLoc
I sure would not have even thought about writing that in this manner:
Code: Select all
set the loc of [myObject] to (item 1, item 2 of the mouseLoc)
Some of the functions appear to work just like that, or how I would expect them too. Others (like the selectedLine) do not appear to work that way at all, and in fact from the previous thread, I get that they do not, so the real question here is how do you tell when a return from a function is going to work like the mouseLoc, and when it is going to act like the selectedLine ?
Another way to put it might be, how do you tell when you are going to have to use a pre-qualifier, like:
Code: Select all
get the text of the selectedLine; put the last word of it into myVar
and when you don't need to use a pre-qualifier...
Code: Select all
set the loc of [myObject] to the mouseLoc
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 11:01 pm
by dunbarx
Bogs.
OK, I see.
I guess you just have to be conversant with the precise "wording"of the result of those functions. The "selectedLine" does NOT return
it basically, as you said, only returns
Why there is not a Bogs-enhanced selectedLine function, "theValueOfTheSelectedLine" is another issue. Why not write one?
Craig
Re: How to tell what a function is returning
Posted: Sun Feb 07, 2021 11:07 pm
by dunbarx
Just for laughs, if you see that there is not enough information in what the "selectedLine" give back, you can force a level of evaluation with:
Code: Select all
on mouseUp
do "answer the last word of" && the selectedLine
end mouseUp
I asked you not to mention "do".
Anyway, if you think through this, the selectedLine is now integrated and attached to "the last word of", to create a string which LC will see exactly the same as all those "text" and "value" inclusions.
Craig
Re: How to tell what a function is returning
Posted: Mon Feb 08, 2021 12:39 am
by bogs
dunbarx wrote: ↑Sun Feb 07, 2021 11:01 pm
I guess you just have to be conversant with the precise "wording"of the result of those functions.
...and that was exactly the answer I was hoping I wouldn't get heh. Oh well, I've been disappointed before, I'm sure I will be again
dunbarx wrote: ↑Sun Feb 07, 2021 11:01 pm
Why there is not a Bogs-enhanced selectedLine function, "theValueOfTheSelectedLine" is another issue. Why not write one?
I gave up on the evil selectedLine and it's ilk, and did exactly that, wrote my own function. To make it even worse, it is a repeat loop function!! ICK!!
but that is for this particular case, and of course, not having 20 years in this language is going to be a disadvantage if there isn't any way to tell what your getting back from a function, as I am sure I will hit this stumbling block over and over and over and...
BTW, I am
not looking for a new feature to be added to this language, and changing it now would I am sure break decades of apps that came before, but
holy cats it would be nice to have one thing work like the next so you could apply what you learn one time over and over and over and...
dunbarx wrote: ↑Sun Feb 07, 2021 11:07 pm
I asked you not to mention "do".
I also had already done the "do", the problem being that I may wind up with too many "do do do do do" in this if I kept along that trail
Re: How to tell what a function is returning
Posted: Mon Feb 08, 2021 7:33 pm
by jacque
I've been using the language for so long that I never think about it, but on reflection I think I'd look at what the function returns. Virtually everything in LC script is a string and the engine manages variable typing for you if it can tell otherwise. If it recognizes integers it will use them as such, and the mouseloc is a list of two integers. The selected line is a combination of integers and text and so remains a string in its internal typing.
Of course I'm guessing, I have no idea what goes on under the hood.
Re: How to tell what a function is returning
Posted: Mon Feb 08, 2021 7:57 pm
by bogs
Yes, I agree with what you've said. I guess what I was / am trying to figure out is why different returns act so differently. Consider these two pictures -
I am pretty sure I could use 'the selectedField' directly, but here is what throws me off. Part of it (where 'no quotes' is) I wouldn't consider a string because the variable doesn't show quotes around it, the second part (the long stack name) *does* have quotes around it, and they are clearly shown, so I'd consider that a string.
The bottom picture shows the return of the selectedLine just like the first part of the picture above it, looking at it, I would never suspect it is a quoted string.
I was hoping to learn how anyone would know? Is there some variable set in the engine that tells you what your getting? If so, it would be nice to be able to test for it, and then be able to handle it correctly. I admire anyone that been using anything so long they never even have to think about it, but for anyone coming in, it can be quite a gotcha if your expecting one thing and get something completely different, and can't even test for it.
Least, thats how it seems to me.